1. Field of the Invention
The present invention relates to a camera module, and more specifically to a camera module having a relatively compact size to be equipped in camera-equipped electronic apparatuses, such as, for example, a cellular phones and the like.
2. Description of the Prior Art
In a camera module having a relatively compact size to be equipped in camera-equipped electronic apparatuses, such as, for example, cellular phones and/or the like, a CMOS sensor or a CCD sensor is used as an image pickup device.
FIG. 4 is a cross sectional view showing a prior art camera module 11. The camera module 11 is composed of a lens unit 12 and an image pickup device portion 13 provided under the lens unit 12.
The lens unit 12 includes a barrel 121 in which an objective lens 123 and a lens 124 are provided and a lens holder 122 in which the barrel 121 is rotatably held. The barrel 121 is moved in a direction of an optical axis when turning the barrel 121 with respect to the lens holder 122, whereby focus adjustment is carried out.
The image pickup device portion 13 includes a base 131 in which an opening 134 having a substantially square shape is formed at the top surface thereof, an IR cut filter 14 provided so as to cover the opening 134, a substrate 16 provided under the base 131 and an image pickup device 15 mounted on the top surface of the substrate 16. In this camera module 11, a CMOS sensor is used as the image pickup device 15.
In the camera module 11, a light path 17 is formed from a barrel opening 126, which will be described later, of the barrel 121 to the image pickup device 15 through the objective lens 123, the lens 124 and the IR cut filter 14. The light path 17 is defined or surrounded by inner peripheral surfaces of the components, such as, for example, the inner peripheral surface of the barrel 121 and the inner peripheral surface of the opening 134 of the base 131 and/or the like. On these inner peripheral surfaces, various step portions are formed so as to protrude toward the light path 17. For example, the barrel opening 126 of the barrel 121 has an outside opening portion 135 having a conically inclined inner peripheral surface, and a lot of step portions, such as, for example, steps 128a to 128e which are formed on the conical inclined inner peripheral surface of the outside opening portion 135 in a stair-like manner. Further, on the inner peripheral surface of the barrel opening 126 of the barrel 121, an annular edge 127 is also formed so as to protrude toward the light path 17. Furthermore, the edges of the base 131 defining the opening 134 also protrude toward the light path 17 to form one of the step portions mentioned above.
Hereinbelow, among these step portions which are formed so as to protrude toward the light path 17, the step portions formed on the inner peripheral surface of the barrel 12 will be described in more detail.
The barrel opening 126 is formed at a center of the upper portion of the barrel 121. The annular edge 127 is one of the step portions formed on the inner peripheral surfaces defining the light path 17. The annular edge 127 serves as a diaphragm for controlling an amount of light and reducing chromatic aberration. The annular edge 127 has a lower annular corner portion (lens side portion) 125 which is formed to have a right angle in its cross section.
The barrel opening 126 also has the outside opening portion 135 which is formed into a shallow conical shape having an inclined inner peripheral surface diverging from the annular edge 127 inwardly with respect to the outside. The outside opening portion 135 also forms one of the inner peripheral surfaces defining the light path 17. On the conically inclined inner peripheral surface of the outside opening portion 128, the steps 128a to 128e are formed in a stair-like manner as described above. These steps 128a to 128e are formed for preventing stray light from being generated at the outside opening portion 128.
The inner surface of the barrel opening 126, namely, the surfaces of the annular edge 127 and the outside opening portion 135 are subjected to staining processing (hereinbelow, simply referred to as “staining” on occasion) for preventing generation of stray light which would be caused by reflection of external light on these surfaces since such stray light becomes cause of generation of ghost image, flare and the like.
However, since the camera module 11 is to be equipped in a cellular phone and the like, it necessarily has a particularly compact size, for example, 6 mm in length, 6 mm in width and 4.5 mm in height. Accordingly, the barrel 121 also has an extremely small size, and thus an extremely small size mold is used for producing the barrel 121. The mold has an annular step portion for forming the lower annular corner portion 125 of the annular edge 127. However, the size of the annular step portion of the mold is extremely small. Therefore, it is very difficult to form very minute irregularities for the staining processing on the annular step portion of the mold appropriately. Namely, since the annular step portion of the mold for forming the lower annular corner portion 125 of the annular edge 127 has a right-angled shape in its cross section, it is very difficult to form minute irregularities for staining on such a right-angled shape portion of the mold surely. This means that minute irregularities by staining cannot be formed on the lower annular corner portion 125 sufficiently, which results in the case that undesirable stray light is generated at the lower annular corner portion 125 whereby generating ghost image, flare and the like.